High aspect ratio, microstructure-covered, macroscopic surfaces

Abstract

The performance of many macroscopic structures (those whose dimensions are on the order of centimeters, meters, or even larger) can be greatly improved by covering their surfaces with microstructures. There are several applications in which "large," microstructure-covered sheets are useful. An apparatus and method are disclosed for forming high aspect ratio microstructures ("HARMs") on planar and non-planar surfaces, using a modification of the LIGA microfabrication process. A free-standing polymer sheet is lithographically patterned with through-holes. The polymer sheet is then pressed against, clamped to, or otherwise attached to a conductive substrate in such a way that the patterned holes in the sheet are not blocked. Subsequent electroplating produces well-defined HARM structures on the planar or non-planar surface, in shapes that are complementary to the lithographically patterned through-holes in the polymer. The polymer may then be removed (e.g., by melting, dissolution, or burning). Various planar and non-planar surfaces have been covered with microstructures. Where the metal surface is non-planar, the polymer sheet may be heated or otherwise made sufficiently flexible to conform to the metal surface, preferably by heat-shrinking to assure firm contact. The process may be used to electroplate microstructures directly onto metal surfaces generally-not just onto metal surfaces that have been specially prepared for LIGA processes, as has previously been the case.

Description

This invention pertains to macroscopic surfaces whose properties are altered by being covered with microstructures, and to an apparatus and method useful in manufacturing such surfaces.The properties of many macroscopic structures depend in large part on their surface properties. For example, the rate of heat transfer between a structure and its surroundings depends on the ease with which radiative, conductive, and convective heat transfer occur between the surface of the structure and the surroundings. As another example, the strength of composite materials is often governed by the strength of the bond between the "internal" surfaces joining the different lamina. As yet another example, the rate of activity of a catalytic surface often depends on its surface area.Efforts have been made to control the interaction of surfaces with their surroundings by painting, roughening, anodizing, hardening, plating, smoothing, and the like. In many cases, the resulting improvements in surface pr...

AI Technical Summary

Benefits of technology

The performance of many macroscopic structures (those whose dimensions are on the order of centimeters, meters, or even larger) can be greatly improved by covering their surfaces with microstructures.

It has been discovered that the performance of many macroscopic structures (those whose dimensions are on the order of centimeters, meters, or even larger) can be greatly improved by covering their surfaces with microstructures. In addition, a novel apparatus and method have been discovered for forming high aspect ratio microstructures ("HARMs") on planar and non-planar surfaces, using a modification of the LIGA microfabrication process. A free-standing, non-conductive sheet (e.g., a polymer or ceramic sheet) is patterned lithographically or by LIGA with through-holes. The non-conductive sheet is then pressed against, clamped to, or otherwise attached to a conductive substrate in such a way that the patterned holes in the sheet are not blocked. Subsequent electroplating produces well-defined HARM structures on the planar or non-planar surface, in shapes that are complementary to the lithographically patterned through-holes in the non-conductive sheet. The sheet may then be removed (e.g., by melting, dissolution, or burning).

Problems solved by technology

Using conventional methods, it is difficult if not impossible to make a heat shield that simultaneously satisfies each of these design considerations.

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